Project Summary In humans, aerosol exposure to Mycobacterium tuberculosis (Mtb) results is disparate outcomes, ranging from no-infection and/or clearance, to progressive disease. Lung-resident, immune effectors likely play a critical role is determining the outcome following exposure to Mtb, yet remain poorly understood. Mucosal associated invariant T (MAIT) cells are an innate-like T cell subset prevalent in humans and enriched in the airway. Human MAIT cells have been defined by the expression of the semi-invariant TCR? chain TRAV1- 2/TRAJ12/20/33 and their restriction by the non-polymorphic MHC class I-like molecule, MHC-related protein 1 (MR1). MAIT cells recognize Mtb and can be activated by small organic molecules, derived from the riboflavin biosynthesis pathway. We have shown that MR1-restricted T cells can use TCRs that are not TRAV1-2, and can recognize organisms that cannot produce riboflavin {Meermeier, 2016}. Consequently, we define MAIT cells as a subset of MR1-restricted T cells (MR1Ts). Furthermore, we find that not all MR1Ts can be defined based on MR1 tetramer bound to the known MAIT agonist / MR1 ligand 5-(2-oxopropylideneamino)-6-D- ribitylaminouracil (5-OP-RU), in that they can be defined based on their MR1-dependent response to microbial infection and binding to alternate MR1 tetramers. We provide evidence for novel, mycobacterially-derived MR1 antigens, and demonstrate that MR1Ts in the lung are characterized by oligoclonal enrichments, possibly driven by these antigens. Finally, we find that lung-resident MR1Ts have anti-microbial effector capacity. These findings raise the intriguing possibility that lung resident, Mtb-reactive, MR1Ts could play a specialized role in the early detection and control of infection due to Mtb. Specifically, this could be the result of the release of pro-inflammatory cytokines such as IFN-?, as well as by their direct anti-microbial activity. In this application, we will use thoracic imaging (PET/CT or traditional radiography) to define the health status of HIV infected and uninfected individuals following exposure to Mtb. Those with clinical TB will be defined by symptomatic disease, abnormal CXR, and culture positivity. Among asymptomatic individuals with a negative CXR, PET/CT will be used to categorize those who are resistant (PET/CT negative) vs those with subclinical disease (PET/CT positive). We hypothesize that lung resident MR1Ts with the capacity to recognize and control infection with Mtb will be associated with favorable clinical outcomes. In this application, we will address the following questions: 1) What is the prevalence and effector function of MR1T cells in the lung and peripheral blood following exposure to Mtb and in the setting of HIV? 2) What is the relationship of MR1T TCR usage and ligand discrimination to outcomes following exposure to Mtb? 3) How might MR1T cells control infection with Mtb? Ultimately, the work from this project would support MR1T cell targeted vaccines and immune-therapies as a means to improve resistance to disease following exposure to Mtb.